Small-data urban adaptation twin: sustainable heat-flood planning in data-scarce fragile cities

Abstract Data-scarce and fragile cities face compound heat and pluvial-flood risks but often lack the sensor-rich and cadastral systems assumed by conventional urban digital twins. This study presents the Urban Climate Triage Twin (UCTT), a lightweight, auditable decision-support workflow that converts public data into field-verification hypotheses for sustainable adaptation. UCTT combines Microsoft building footprints, a corrected two-tile SRTM terrain mosaic, WorldPop exposure and NASA POWER climate-product indicators with explicit heat, flood and vulnerability scores and five scale-comparable intervention benefits. The Taiz, Yemen demonstrator screened 1,011,910 footprint detections, retained 191,662 by coordinate screening, estimated 23.57 million m² of plausible roof area and analyzed 3653 daily records for 2015–2024. The NASA POWER maximum of 369.2 mm is treated only as a gridded-product flag, not a gauge observation or design rainfall depth. Exact deterministic ranking selects the 100 highest-priority cells (4.94% of 2025): 49 cool-roof, 16 shade-access, 17 micro-drainage, 10 permeable-detention and 8 emergency-access cells. An untuned equal-weight baseline yields Spearman ρ = 0.901 and shares 68 cells. Selected cells are substantially higher in heat, flood, exposure, built intensity and compound score, whereas terrain stress alone is not significantly separated ( p = 0.305), evidence consistent with the intended compound-selection logic. UCTT is therefore a reproducible small-data decision twin for adaptation triage, not a substitute for independent local hydraulic, thermal, tenure or engineering verification.